A conventional slide fastener generally comprises a pair of support tapes having confronting edges provided with rows of coupling elements which may be interconnected and formed by a continuous synthetic-resin monofilament. These coupling elements can be affixed to the tape by stitching or various other means, generally involving the interposition of a textile thread between the coupling elements or the coupling heads formed thereby. The coupling heads may be deformed to provide protuberances which engage behind the protuberances of a pair of coupling heads of the opposite row.
An important characteristic of such slide fasteners, whether the row of coupling elements is a coil or a meander, is the ability of the slide fastener to resist transverse stresses which tend to spread apart the coupling elements and cause release of the coupling head received between them.
Generally the slide fastener must be capable of resisting longitudinal stresses which arise upon stretching of the article in which the slide fastener is incorporated, transverse stressing in the plane of the slide fastener which tends to open the gap spanned by the slide fastener, transverse stress orthogonal to the plane of the slide fastener, and torsional stresses which arise upon twisting of the slide fastner. While various head configurations have been proposed to resist the transverse and longitudinal stresses mentioned above, the importance of resisting torsional stress has come to the fore only recently.
Torsional strength is the strength with which the slide fastener resists separation upon the application of torque between coupling elements about the longitudinal axis of the slide fastener. It will be appreciated that all of the other stresses can give rise to torsional stress in a sense and that torsional stress can also result in longitudinal and transverse stress. In any event, the principal characteristic of torsional stress is the tendency of such stress to deflect each couping head out of engagement with the other coupling element in a plane transverse to the longitudinal axis of the coils.
The stresses arise when a slide fastener is used, for example, in garments or the like and can result from acceleration in centrifugal machines such as extractors, dryers or washers as well as dry-cleaning machines and the like. The torsional resistance or torsional strength of the slide fastener can be increased by increasing the length of the shanks of the coupling elements as is the case when strip fasteners are provided. The copending applications mentioned above are directed at least in part to such fasteners.
Strip fasteners, for the purposes of the present invention, are slide fasteners in which the shanks of the coupling elements reach entirely across the width of the tape-like units in which they are formed at least in part as a weft, the shanks lying in pockets formed by longitudinal threads which cross over from side to side between these shanks. Since the shanks extend across the width of the strip, their bights which interconnect the shanks of adjacent coupling elements can form ridges, as described in the aforementioned applications, to guide a slider.
Of course, the strip fasteners can be stitched directly to a garment, in which case the stitches are applied along the shanks and between them. Alternatively, the strip fasteners can be integrated with respective support tapes with corresponding longitudinal threads which, however, can have a textile weft filament looping around the turns of the coupling element.
The latter systems can distinguish from the conventional arrangements in which a textile thread is interposed between successive coupling elements and which are susceptible to dimensional changes because of shrinkage or the like of the interposed textile threads.